1. Field of the Invention
The present invention relates to a paper feeding apparatus for transporting documents to an image reading apparatus or the like, and especially to the arrangement of a document separating roller and a feed roller of the paper feeding apparatus.
2. Description of the Related Art
In a general image forming apparatus, an automatic document feeder (ADF) is attached as a paper feeding apparatus for transporting documents stacked on a document feeding tray to a reading unit.
Both sides of the documents stacked on the document feeding tray of the ADF are controlled by document guides. When the start button provided on a control panel is pressed, a pick-up roller of the ADF descends and starts rotating at the same time, and the documents are then fed into the ADF.
The fed documents are separated into one-by-one and are transported to the downstream by a document separating apparatus comprised of a separate roller and a retard roller, for example. In the downstream of the document separating apparatus, a plurality of feed rollers for transporting the documents to the reading unit are disposed in the direction perpendicular to the transporting direction of the documents (width direction of the documents), and the documents are transported to the reading unit.
Further, the ADF is constructed capable of transporting the documents of various sizes, and for example, corresponds to the sizes of such as the letter size, the legal size or the Japanese Industrial Standards (JIS) of A5 to A3.
Moreover, for example, a transportation method (side registration method) to set one of the side sections of the document transporting path as a standard line is adopted for the paper feeding apparatus transportation method.
In the ADF of the side registration method, the separate roller is disposed at a position in the orthogonal direction against the document transporting direction, a certain distance away from the standard line. A plurality of feed rollers are disposed at a position in the orthogonal direction against the document transporting direction in the downstream of the separate roller, a certain distance away from the standard line.
Furthermore, the centerline of the separate roller in the orthogonal direction against the document transporting direction corresponds to the centerline of a plurality of feed rollers in the orthogonal direction against the document transporting direction.
By aligning the center of the separate roller and the center position of a plurality of feed rollers, and by disposing appropriately the separate roller and the feed roller a certain distance away from the standard line likewise, the separate roller and the feed roller are capable of being contacted against the documents of various sizes, and the transportation of the documents of various sizes can be carried out.
In the manner stated above, by aligning the center position of the separate roller and the center position of the feed roller, and by disposing the separate roller and the feed roller a certain distance away from the standard line, for example, the documents of various sizes such as letter size, legal size or the Japanese Industrial Standards (JIS) A5 to A3, can be fed to the reading unit.
However, in the case the separate roller and the feed roller are disposed at a position capable of transporting the documents of various sizes by aligning the center lines in this manner, out of the documents of the transportable sizes, concerning the documents of small sizes such as the Japanese Industrial Standards (JIS) A5, only a part of the pick-up roller and the feed roller are to overlap the document.
Therefore, since the transporting force applied to the document is not balanced in the width direction, there are problems in which the skew of the documents generates.
To allow the documents of small sizes to be transported straightly, by displacing the separate roller and/or the pick-up roller toward one side of the width direction of the document, the problems mentioned above can be solved.
However, concerning the documents of large sizes, when the pick-up roller is contacted against the documents, the contacting position of the pick-up roller against the documents is to be greatly displaced from the center of the document width. As a result, the documents are to be skewed while contacting, and the documents are to be fed skewed even more by the start of the rotation of the pick-up roller.
To prevent this, there are paper feeding apparatuses comprising a skew correction roller for correcting the documents fed in skew. However, there are problems that the structure is complicated, the number of parts and the cost increase, and the productivity is low.